1. Field of the Invention
The present invention relates to a process for preparing higher oxo alcohols by hydroformylation of olefin mixtures, which includes selective hydrogenation of the hydroformylation mixtures and recycling of the unreacted olefins.
2. Discussion of the Background
Higher alcohols, and particularly those having 6 to 25 carbon atoms, may be prepared by the catalytic hydroformylation (or oxo reaction) of olefins having one less carbon atom and subsequent catalytic hydrogenation of the aldehyde- and alcohol-containing reaction mixtures. The alcohols are predominantly used as starting materials for the preparation of plasticizers or detergents.
The type of catalyst system and the optimum reaction conditions for the hydroformylation depend upon the reactivity of the olefin used. The dependence of the reactivity of the olefins on their structure is described, for example, by J. Falbe, New Syntheses with Carbon Monoxide, SpringerVerlag, Berlin, Heidelberg, N.Y., 1980, pages 95 ff. The varying reactivity, especially that of the isomeric octenes, is likewise known (B. L. Haymore, A. van Hasselt, R. Beck, Annals of the New York Acad. Sci., 415 (1983), pages 159-175). Industrial olefin mixtures that are used as starting materials for the oxo synthesis include olefin isomers a variety of structures and different having degrees of branching, different positions of the double bond in the molecule and different carbon numbers as well. This applies especially to olefin mixtures that have been produced by dimerization, trimerization or further oligomerization of C2-C5 olefins or other easily accessible higher olefins or by co-oligomerization of said olefins. Examples of typical isomeric olefin mixtures that can be reacted by rhodium or cobalt-catalyzed hydroformylation to give the corresponding aldehyde mixtures and alcohol mixtures include tripropenes, and tetrapropenes and dibutenes and tributenes.
The rate of the hydroformylation reaction decreases with increasing carbon number and with the degree of branching. The reaction rate of linear olefins can be greater than that of the branched isomers by a factor of 5 to 10. The position of the double bond in the olefin molecule also influences the reactivity. Olefins having a terminal double bond react markedly more rapidly than do isomers having the double bond in the interior of the molecule. Because of the differing reactivity of the olefin isomers, relatively long reaction times are required to achieve the highest possible conversion of the olefins. As a result, however, the product yield is decreased due to unwanted side reactions and secondary reactions. The same thing occurs if attempts are made to shorten the reaction times by higher reaction temperatures. Because of the varying reactivity of the isomers, it is especially difficult to achieve high conversion rates and simultaneously high selectivities in the hydroformylation of olefin mixtures.
An object of the invention is to provide a process for preparing higher oxo alcohols from the corresponding olefin mixtures, which combines high conversion rates with high selectivities and, in particular, high space-time yields.
These and other objects have been achieved by the present invention, which provides a process for preparing higher oxo alcohols, including hydroformylating a mixture of isomeric olefins having 5 to 24 carbon atoms in the presence of a catalyst in one stage, wherein the olefin conversion rate for one passage to is restricted to 40 to 90% to produce a reaction mixture, and selectively hydrogenating the reaction mixture, to produce a hydrogenation mixture.
Another embodiment of the present invention provides a composition, which includes a hydrogenation mixture produced by a process for preparing higher oxo alcohols, including:
hydroformylating of a mixture of isomeric olefins having 5 to 24 carbon atoms in the presence of a catalyst in one stage, wherein the olefin conversion rate for one passage to is restricted 40 to 90% to produce a reaction mixture, and
selectively hydrogenating the reaction mixture, to produce the hydrogenation mixture.